Rethink on effect of Antarctic ice-melt on sea levels

Updated
October 22, 2012 19:26:00

Scientists using satellite technology have discovered that the effect of melting ice in Antarctica on sea level rise is less than earlier thought. But the sea level rise could spike if there's a change in snow rates in east Antarctica.

BRENDAN TREMBATH: Scientists have found that melting ice in Antarctica is contributing less to sea level rise than previously thought. The scientists used a satellite to estimate the weight of the land mass of Antarctica and how it has changed.

Felicity Ogilvie reports from Hobart

FELICITY OGILVIE: Scientists have known for a couple of decades that ice in Antarctica has been melting, and causing sea levels to rise. Now, they've got their clearest picture yet of exactly how much water is flowing off the ice shelves.

In an article published in today's edition of the journal Nature, they say over the past decade, ice loss from Antarctica has been contributing 0.2 millimetres a year to sea level change.

One of the researchers, Professor Matt King from the University of Tasmania says that's lower than previous estimates.

MATT KING: It's at the lower end of what various other groups using different approaches have suggested. There's been a fairly wide scatter of results, most of them suggesting Antarctica's contributing something to sea level, but our estimate came at the lower end.

And indeed, those who have been using the same data set as us are significantly lower than those other estimates so it moves the weight of the evidence if you like to a small Antarctic present-day contribution.

FELICITY OGILVIE: So if Antarctica's not causing sea level rise, what is?

MATT KING: So a lot of the sea level rise is coming from thermal expansion, so the oceans are getting warmer and they heat up and they expand. There's also a large input from Greenland, so Greenland is contributing a lot to sea level change. And the small glaciers that are scattered all around the globe have also been receding and melting and adding to sea level change as well.

FELICITY OGILVIE: Professor King says that one reason why Antarctica isn't contributing as much as expected to sea level rise is that while ice is melting in the west of Antarctica, snow is falling in eastern Antarctica.

MATT KING: If you didn't have the heavy snowfalls in the east anymore you would, which was offsetting this mass loss in the west, then you would basically double or thereabouts the contribution of Antarctica to sea level.

If you then add on the potential for it to continue to accelerate in its mass change then Antarctica could be beginning to contribute quite a lot in the future. And that's very uncertain exactly how that will happen. But one glacier in Antarctica has been suggested could contribute up to seven centimetres of sea level change.

FELICITY OGILVIE: While the full effects of the ice melt are still unknown, a push is on to protect the oceans surrounding Antarctica. Australia and France are trying to convince a group of 23 other nations to create new marine reserves system in Antarctica.

Tony Fleming is heading Australia's delegation to the international antarctic organisation CCAMLR (Commission for the Conservation of Antarctic Marine Living Resources) that is meeting in Hobart this week. He says the proposal for the new reserves covers almost two million square kilometres of the ocean in east Antarctica.

TONY FLEMING: In east Antarctica there's an MPA (Marine Protected Area) which will protect nursery areas of krill and toothfish for example, a number of the MPAs will protect the foraging grounds of penguins and marine mammals.

They're big because they need to be big. The proposals are big because they need to be big because penguins forage over a wide area and marine mammals forage over a wide area.

FELICITY OGILVIE: Fishing will still be allowed in the marine reserves but it will be regulated under the Antarctic treaty system. The reserves will protect feeding areas for whales, but there's no provision to stop whaling.